Development of an auto-focus system based on the moiré method

Ju Yi Lee, Yung Hsing Wang, Lyu Jhen Lai, Yu Ju Lin, Yu Hsiu Chang

Research output: Contribution to journalReview articlepeer-review

18 Scopus citations


An auto-focus system based on the moiré effect and a feedback control method is presented. First, a collimated laser beam passes through a focusing lens then falls incident on the surface of the sample. The deviation of the angle of the light reflected back is proportional to the defocus distance from the sample. The reflected light then passes through two spiral gratings, producing three types of moiré pattern which can be observed and recorded by a linear CCD. The defocus distance can be derived from the spiral angle in the moiré pattern. The results show that auto-focusing can be achieved by the moiré method for glass and mirror samples in a cycle time of less than 0.1 s.

Original languageEnglish
Pages (from-to)1793-1800
Number of pages8
JournalMeasurement: Journal of the International Measurement Confederation
Issue number10
StatePublished - Dec 2011


  • Auto-focus
  • Moiré
  • Spiral grating


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